Currently, popular mobile phones often have a touch panel. However, touch panels have high power consumption, and there has been a problem in reducing the continuous operating time of mobile phones. Accordingly, as a power-saving technology related to the mobile phones equipped with touch panels, there is a technology in which, for example, the power supply is stopped when it is detected that the mobile phone is held by hand and placed against a user's ear during a telephone call. With such technology, it can be expected that power consumption during the telephone call is reduced and a duration of a telephone call can be prolonged. However, a display screen may not be operable because a power supply to the display screen may be terminated during the telephone call, so various required functions such as volume adjustment and recording functions generally cannot be performed during the telephone call by touch panel operation. Moreover, when performing, for example, volume adjustment or the recording function during the telephone call, it is necessary to move the mobile phone away from the ear before doing so, reducing convenience for the user.